Currently, there are several companies that sell circular forms for manhole rehabilitation. These forms are generally constructed of plastic or steel. The process of manhole rehabilitation consists of first erecting the form within an existing manhole structure and then filling the space between the outer surface of the form and the existing manhole structure with concrete, creating a new concrete liner in the space.
As with any type of concrete placement, concrete consolidation is vital to a quality finished product. In the past, concrete has been consolidated by using eccentric cam internal vibrators which had to be inserted into the actual concrete. This creates a large number of problems in this particular forming situation due to:
1) the fact there is only 1-4 inches of space between the form and the existing manhole structure; PA1 2) the difficulty involved in feeding the vibrator head past the corbel area of the form; and PA1 3) the lack of visual confirmation of consolidation usually seen in normal forming situations.
Several examples of such vibrators are disclosed in U.S. Pat. Nos. 3,726,508 (Varnello); 3,551,967 (Williams); 3,470,279 (Abbott); and 3,771,769 (Niemi).
Unfortunately, all of these prior art devices have the various disadvantages mentioned above.